It has been recognized that a positive displacement drilling motor, such as a Moineau-type device which has a spiral rotor that rotates within a lobed stator, has a maximum mechanical power output. When this power output is exceeded, any additional hydraulic power that is furnished to it is dissipated by deformation of the stator. Once the stator is being deformed, there is an increase in wear thereof, and the rate at which the bit penetrates the rock is reduced. Since mechanical power output is related to the amount of hydraulic power that is input to the motor, there is a need to compare such hydraulic power input with the mechanical power output so that maximum mechanical power output can be identified and tracked in real time. The measurement of variables upon which these parameters depend, such as weight-on-bit (WOB), torque, motor shaft speed and pressure drop across the motor's power section, preferably are made downhole and in a continuous manner so that they are representative of actual values. Such measurements are transmitted uphole by a measuring-while-drilling (MWD) tool for processing and display at the surface substantially in real time. Based upon such calculations and display, mechanical power output and thus the rate of penetration of the bit can be maximized while reducing wear on the stator to a minimum, in accordance with this invention.
A broader object of the present invention is to provide a new and improved process for optimizing the drilling of a well with a downhole motor.
Another object of the present invention is to provide new and improved processes for drilling a well with a downhole motor which optimize the rate of penetration of the bit while minimizing wear on the stator of the motor.
Still another object of the present invention is to provide new and improved methods and systems for comparing hydraulic power input to a drilling motor to its mechanical power output so that stator wear can be kept at a minimum while optimizing the rate of penetration of the bit through the rock.